l. Field of the Invention
The present invention relates generally to a traction control system for an automotive vehicle which controls throttling and/or braking operations to modify driving forces transmitted to driven wheels upon occurrence of wheel slippage during acceleration. More particularly, the invention relates to an improved arrangement for determining a degree of wheel slippage which may be utilized for traction control of an automotive vehicle.
2. Description of the Prior Art
Japanese Patent First Publication No. 1-138333 discloses a traction control system for an automotive vehicle. This traction control system corrects right and left compliance wheel speeds respectively based on previous speed data detected in a preceding program cycle and current speed data to determine an average value of the corrected right and left compliance wheel speeds. Based on a difference between the average value of the compliance wheel speeds and driven wheel speed, wheel slippage during acceleration is determined. When the driven wheels slip, the system performs throttling control to reduce engine power so that the wheel slippage is restricted to resume traction of the driven wheels against a road surface.
However, in the above prior art traction control system, when failure occurs in either one of wheel speed sensors of the right and left compliance wheels due to wire breakage or short circuit, for example, a wheel speed value output from the defective sensor will become substantially zero, resulting in the average value of the right and left compliance wheel speeds being decreased greatly, which will cause the wheel slippage to be determined to be much greater than an actual wheel slippage. Thus, the system reduces driving force undesirably, degrading acceleration characteristics.
For avoiding the above drawback, a greater one of the right and left compliance wheel speeds may be used to determine a compliance wheel reference speed. This, however, encounters a drawback in that even when the sensors are normally operating, the compliance wheel reference speed may become too great due to the difference in turning radius between inside and outside wheels, noise input to the sensors, or the difference in diameter between right and left tires such as when a tempa space tire is mounted on one of the wheels, an mount of wear is different between the tires, or one of the tires is punctured.